Chair backrest support



FIG. 1 is a perspective view showing a front, top and right side of the chair backrest support;

FIG. 2 is a perspective view showing a back, top and left side of the chair backrest support;

FIG. 3 is an elevational view of the right side of the chair backrest support;

FIG. 4 is an elevational view of the left side of the chair backrest support;

FIG. 5 is a front elevational view of the chair backrest support;

FIG. 6 is a rear elevational view of the chair backrest support; and,

FIG. 7 is a top plan view of the chair backrest support. 

The ornamental design for a chair backrest support, as shown and described. 